Valve mechanism for unloading compressors



- 15 in the receiver drops to a value Patented Mar. 11, 1941 VALVEMECHANISM FOR UNLOADIN COMIPRESSORS A Burns Dick, Ferguson, ElectricCorporation, 1 tion of Delaware Mo., assignor to Wagner St. Louis, Mo.,a corpora- Application November 8, 1939, Serial No. 303,380

. 4 Claims. My invention relates to compressors and more particularly toa valvemechanism 'for causing the compressor to be unloaded. One of theobjects of my invention is to provide an improved valve mechanism whichis automatically operable to unload a compressor when the pressure inthe receiver of the compressor is a predetermined value. Another objectof my invention is to produce an unloading valve mechanism which will bequick acting to unload the compressor when the pressure in the receiveris a predetermined value and also quick acting to place the compressoragain in operation when the pressure below said predetermined value.

Other objects of my invention will become apparent from the followingdescription taken in connection with the accompanying drawing in whichthe single figure is a view, partly in section, showing a compressorhaving associated therewith an unloading valve mechanism embodying myinvention.

Referring to the drawing in detail, the rotary compressor is of knownconstruction and comprises a stator I having eccentrically mountedtherein a rotor 2 secured to a drive shaft 3 journaled in the end plates4 and 5. The rotor 2 is provided with a plurality of spaced slots' 5extending in an axial direction in which are mounted reciprocable blades1 (one only being shown) biased outwardly into engagement with the innersurface of the stator by springs 8. The end plate 4 is provided with anintake passage 9 and the end plate 5 with an outlet passage III. Se-

cured to the end plate 5 is an oil reservoir or dome I I which containsoil for the purpose of lubricating the compressor. In the constructionshown the shaft 3 of the compressor drives an oil pump l2 to pump oilfrom the body of oil through passage l3 and discharge it into a well l4through the opening IS. The oil in the well is free to flow through thepassage It in shaft 3 and then into the compressor by way of the keywayl1 to-thus provide lubrication for the movable parts of the compressor.In order that the oil may be forced into the compressor under pressureduring operation of the compressor, the body oi oil in the oil dome iscaused to be subject to the fluid under pressure discharged from thecompressor. This is accomplished by having the discharge port Iconnected to apipe II which extends above the oil line. An oil separatorl3 removes any excess oil which may be as discharged from the compressortogether with the compressed air. The discharge port It! has associatedtherewith a check valve 20 for preventing any of the compressed air fromreturning to the compressor. The oil dome communicates-with thecompressed air receiver or tank 2 I. by a conduit 22 and a check valve23 prevents return of compressed air to thedome. The compressed air maybe used for any purpose de: sired, as for example, the actuation ofvehicle brakes.

In accordance with my invention, I provide an improved valve mechanismgenerally indicated by the numeral 24 by which the intake of thecompressor can be shut ofi and the oil reservoir vented to atmosphere tothereby com- 15 pletely unload the compressor. The valve mechanismcomprises two casings 25 and 26 bolted together and mounted on thecompressor as a unit adjacent the intake passage 9.

The casing 25 is provided with a passage 21 for placing the intakepassage 9 in communication with the atmosphere through an air cleaner 28mounted on casing 25. The passage 21 has associated therewith a valveseat 29 and cooperating therewith is a movable valve member 2530positioned in a chamber 3| formng an extension of the passage 21. Thevalve member is guided in its movement by a guide sleeve 32 which alsoacts as a stop against which the valve is normally held open by a lightspring 33. The 30 valve member is adapted to be moved to closed positionagainst the bias of the spring by a fluid motor which comprises abellows 34 secured to the valve member at one end and clamped at theotherend to the wall of the 35 chamber 3| by a perforated nut 33 wherebythe bellows can communicate with a chamber 36 at the connection betweenthe two casings 25 and the air cleaner. The valve element 42 is mount-60 ed on a fluted valve stem 43 which extends through the bore 39 intothe chamber 38. This valve element is normally biased to closed positionby a light spring 44, thus sealing the oil reservoir from atmosphere.The valve element 42 is'moved to open position by a fluid motor also inthe form'of a bellows 45 which is situated in the chamber 38. One end ofthe bellows is secured to the stem 43 and the other end to the wall ofthe chamber by a perforated nut 45 which permits the bellows tocommunicate with the previously mentioned chamber 36.

The casing 26 is provided with a cylindrical bore 41 open to atmosphereand with a chamber 49. A passage 49 connects the bore with chamber 36and a second passage 50 and conduit 5| places the bore in communicationwith the air tank 3|. A spool-type valve member 52 is reciprocablymounted in the bore 41 and is provided with a stem 53 extending into thechamber. The end of the stem carries a cup-shaped member 54 andcooperating therewith is a. spring 55 which normally biases the valve.stem and valve 52 to such a position in the bore that the passage49'leading to the chamber 36 will be in communication with theatmosphere through an air cleaner 56 in the open end of the bore. Thisposition of the valve also prevents any communication between thepassage 50 and 49. The valve 52 is actuated by a fluid motor in the formof a bellows 51 lying in the cup-shaped member 54 and having one endsecured to the stem 53 and the other end sealed to the wall of thechamber 48 by a closure plug 58. The interior of the bellows is inconstant communication with the air tank by a conduit 59. The spring 54is of predetermined strength and is capable of maintaining the valve 52in the position shown whereby passage 49 communicates with atmosphere aslong as the tank pressure is less than a predetermined value, say forexample, ninety pounds per square inch. When the pressure is exceeded,

the valve will begin to be moved and thenconnect the passage 49 to theair tank when the air tank pressure reaches a higher value, as forexample, one hundred pounds per square inch which is sufficient tocompress the spring 55 the required amount.

Referring to the operation, the parts assume the positions shown whenthe compressor is operating and the tank is at a pressure below ninetypounds per square inch. Under these conditions air enters the compressorthrough the air cleaner 28, the open valve member 30 and then throughpassages 21 and 9. The compressed air is forced out into the oilreservoir through the check valve 23 and by way. of conduit 22.

The valveelement 42 is closed and the oil reservoir is closed. Thepressure in the oil reservoir will be substantially the same as thepressure in tank 2i. Due to the pressure in the oil reservoir,

I the oil in well 14 will be under pressure and thus be forced into thecompressor to properly lubricate the same. Any oil carried bythecompressed air will return to the reservoir.

When the pressure in the air tank reaches the value of ninety pounds persquare inch, the bellows 51 will begin to expand and compress spring 55whereby the spool valve: 52 will be moved toward the right. As pressurecontinues to be built up and the valve moved, passage 49 will be cut offfrom atmosphere; When the pressure .in the tank reaches approximatelyone hundred pounds per square inch, the valve 52 will have been movedsuch a distance that the passage 49 will be placed in communication withthe air tank. This will cause the air tank pressure to be effective onboth bellows 34 and 35 causing them to quickly expand. Consequently, thevalve member 30 will be immediately closed and the valve member 42immediately opened, thereby closing the intake to the compressor andventing the oil reservoir to atmosphere.

The compressor will now be substantially completely unloaded. No moreair will be drawn into the compressor. Any air that is in the compressoror which may leak in will be easily forced out through the dischargeport Ill since there is no pressure other than the spring of the checkvalve acting to hold the check valve closed and against which thecompressor must work. If the oil reservoir were not vented, the air inthe compressor could not be easily forced out-the discharge port andconsequently, some air would remain in the compressor and becontinuously circulated and recompressed. The compressor will now runfree and perform no work, thus requiring a'minimum of power to turn it.Also since the blades 1 are doing no compressing, they will move freelyin their slots and have little wear.

With the oil reservoir vented to atmosphere when the compressor inlet isclosed, the oil in well l4 will'no longer be forced into the compressorby a to the compressor will only be that which flows in under the actionof gravity and that which may be pulled in by of the compressor. Thisamount of oil is sufficient for lubricating the idlingcompressor but notsuch an amount that the compressor will choke up with oil as would bethe case if the oilreservoir were not vented and oil were continued tobe forced in under a high pressure.

When air is used from the air tank, the pressure therein will drop. Thispermits the valve 52 to move to the left under the action of spring 55.When the pressure reaches ninety pounds per square inch, the spring willhave moved the valve to such a position that the passage 49 will beconnected to atmosphere. This will cause a release of the air pressureacting on the two bellows 34 and 45 and permit the valve member 30 to beopened by spring 33 and the valve element 42 to be closed by spring 44.Air can now again be drawn into the compressor and then forced into thetank in a manner already described since the oil reservoir is sealed.

Being aware of the possibility of modifications in the particularstructure herein described without departing from the fundamentalprinciples of my invention, I do not intend that its scope be limitedexcept as set forth by the appended claims. Y

Having fully described my invention, what I claim as new and desire tosecure by Letters Patent of the United States is:

1. In combination with a compressor provided with an intake port and adischarge port, a storage receiver for receiving compressed fluid fromthe compressor, a check valve between the compressor discharge port andthe receiver, automatically operable means for closing the intake portand connecting the discharge port to the source of fluid to becompressed, said means comprising a normally open valve for the intakeport, a fluid motor for closing the valve, a normally closed valve forplacing the discharge port in communication with the atmosphere, asecond fluid motor for opening the last named valve, means including aslidevalve for placing both fluid motors in communication with thereceiver or with the atmosphere, said valve havinga position in whichthe fluid motors are not connectedwith either the receiver oratmosphere, 8.

the partial vacuumrin parts matically operable means for closing theintake port and connecting the discharge port to the source of fluid tobe compressed; said means.com-' prising a valve for the intake port, aspring for, biasing the valve open, a bellows-type fluid motor connectedto the movable element of the valve, means including a second valve forconnecting the discharge port to atmosphere, a spring forbiasing saidvalve closed, a bellowstype fluid motor connected to the movable elementof the second valve, and means for causing fluid pressure from thereceiver to operateboth fluid motor-s when the pressure in said receiveris a predetermined value.

3. In combination with a compressor provided with an intake port and adischarge port, a storage receiver for receiving compressed fluid fromthe compressor, a check valve between the compressor discharge port andthe receiver, automatically operable means for closing the intake portand connecting the discharge port-to the source of fluid to becompressed, said means comprising a valve for the intake port, a springfor biasing the valve open, a bellows-type fluid moreceiver.

a 4; In ,-combination with a rotary compressor 1,

tor connected to'the movable element of the a valve, means including asecond valve for connecting the dischargeport to atmosphere, a springfor biasing said valve closed, a bellowstype fluid motor connected tothe movable element of the second valve, means comprising a third valvefor simultaneously connecting both fluid motors to the receiver or toatmosphere, a spring for biasing said third valve to a positionconnecting the motors to atmosphere, and i a fluid motor operable by apredetermined pressure in the receiver for moving the last named valveto a position to connect the motors to the provided with an intake portand a discharge port and having associated therewith'an oil reservoir'communicating with the compressor for providing lubricant for theworking parts of the compressor and wherein the oil in the reservoir 2is subject to the discharged compressed fluid from the compressor priorto passage through,

a check valve to a receiver, automatically operable means for closingthe intake port and venting the oil reservoir to atmosphere, said means2 comprising two valves one of which is normally open and the othernormally closed, a fluid motor associated with each valve, and meansincluding a pressure-controlled third valve of the slide type forsimultaneously causing one fluid 3 motor to close the normally openvalve and the other fluid motor to open the normally closed valve whenthe fluid pressure in the receiver is a predetermined value.

BURNS DICK. 3

